This invention relates generally to sulfurized phenols useful as antioxidants and, more specifically to the preparation of a liquid, partially sulfurized, hindered phenol composition which is an effective antioxidant in lubricating oils without causing excessive copper corrosion.
The preparation of a liquid lubricant oil additive mixture of 45-75 wt % ortho-alkylphenol and certain amounts of mono, di, tri and tetrasulfides of the phenol by the reaction of the phenol with elemental sulfur using an organic amine catalyst is disclosed in U.S. Pat. No. 3,929,654. It is also reported in this patent that sulfurized alkylphenols prepared by reacting an alkylphenol with sulfur mono- or dichloride tend to cause copper corrosion probably due to the presence of corrosive sulfur species such as sulphochlorinated alkyl phenol.
We have now unexpectedly found that a sulfurized, hindered alkyl phenol composition which is an effective antioxidant with acceptable copper corrosion properties can be prepared by using certain proportions of a sulfur chloride.
In accordance with this invention, there is provided a liquid, partially sulfurized, hindered phenol product prepared by the process comprising reacting a liquid mixture of phenols, at least about 50 weight percent of said mixture consisting of one or more reactive, hindered phenols, with a sulfur chloride in proportions to provide from about 0.3 to 0.7 gram atoms of sulfur per mole of reactive, hindered phenol, and recovering the liquid product.
Also provided are lubricating oil and fuel compositions containing antioxidant effective amounts of the above liquid, partially sulfurized, hindered phenol product.
An advantage of this invention is the liquid nature of the sulfur-bridged, alkylphenol product which facilitates its handling and dissolving in fuels, lubricating oils and other oxygen sensitive materials. The initial phenol mixture to be sulfurized should contain at least two different phenols at least one of which is a hindered phenol having at least one hydrogen in the ortho or para position to the hydroxyl group in proportions to provide a liquid product at ambient temperatures (20.degree. C.-25.degree. C.) from which solid material will not separate on standing. By hindered phenol is meant that the phenol is substituted in at least one ortho position with a branched chain C.sub.3 to C.sub.12 alkyl group and preferably a C.sub.4 -C.sub.6 alkyl group. Examples of suitable ortho-alkylphenols include:
2-tert-butylphenol PA1 2,6-di-tert-butylphenol PA1 2,4-di-tert-butylphenol PA1 2-isopropylphenol PA1 2,6-diisopropylphenol PA1 2,4-diisopropylphenol PA1 2-sec-butylphenol PA1 2,6-di-sec-butylphenol PA1 2,4-sec-butylphenol PA1 2-tert-hexylphenol PA1 2,6-di-tert-hexylphenol PA1 2-tert-butyl-p-cresol PA1 2-tert-butyl-o-cresol PA1 2-tert-dodecylphenol PA1 2-tert-dodecyl-p-cresol PA1 2-tert-decyl-o-cresol PA1 2-tert-butyl-6-isopropylphenol
Suitable mixtures contain at least about 50 weight percent, preferably from about 70 to 90 weight percent, of one or more reactive hindered phenols with the remainder, if any, being one or more other phenols. By a reactive phenol is meant a phenol having at least one hydrogen in the ortho or para position to the hydroxyl group. The mixture more preferably contains at least about 50 weight percent, and most preferably from about 70 to 85 weight percent, of a di-ortho, branched chain alkyl phenol such as 2,6-di-tert-butyl phenol.
The phenolic mixture is reacted with a sulfur chloride, e.g. sulfur mono- or dichloride, in an amount of sulfur chloride to provide from about 0.3 to 0.7 gram atom of sulfur per mole of reactive phenol in the mixture. For sulfur monochloride, this is equivalent to only about 0.15 to 0.35 moles of sulfur monochloride per mole of phenol which is significantly less than a stoichiometric amount. These proportions provide an effective sulfurized antioxidant which has good copper corrosion properties. At least about 30 weight percent, and usually from about 40 to 75 weight percent of the reactive phenols in the partially sulfurized product mixture remain unreacted.
The sulfurization reaction is exothermic and the reaction temperature is preferably kept at from about 15.degree. C. to 70.degree. C. (most preferably from about 35.degree. C. to 55.degree. C.) by cooling and/or by controlling the rate of sulfur chloride addition to the phenolic mixture. The addition usually takes from about 1 to 3 hours. Heat may be added to finish the reaction and keep the temperature within the preferred range. Higher or lower temperatures can be used so long as the reaction is completed without decomposing the product or producing a significant amount of side products. The product can be recovered either by vacuum stripping or purging the reaction mixture with an inert gas and then, optionally, filtering the mixture.
The liquid antioxidant product has a sulfur content of preferably from about 5 to 8 wt percent and includes, depending upon the phenols in the initial mixture, mixtures of sulfur bridged bis and/or polyphenol compounds having from 1 to 6 or more sulfur atoms per bridge.
The products are added to lubricating compositions or liquid organic fuels in antioxidant effective amounts which generally range from about 0.05 to 5.0 wt percent, and preferably 0.1 to 2.0 wt percent, based on the total weight of composition.
The products can be added to the oil or fuel in the form of additive concentrates usually containing a diluent oil or solvent and other additives. The amount of product in the concentrates will generally vary from about 0.5 to 50 weight percent or more.
Lubricating composition base stock oils include natural and synthetic oils having viscosities which generally range from about 2.5 to 12 cps at 100.degree. C. depending upon the particular lubricant application. The compounds of the invention are especially useful in crankcase lubricants where they act as antioxidants and reduce sludge formation.
Advantageous results also are achieved by employing the antioxidant additives of the present invention in base oils conventionally employed in and/or adapted for use as power transmitting fluids such as automatic transmission fluids, tractor fluids, universal tractor fluids and hydraulic fluids, heavy duty hydraulic fluids, power steering fluids and the like. Gear lubricants, industrial oils, pump oils and other lubricating oil compositions can also benefit from the incorporation therein of the additives of the present invention.
The additives of the present invention may be suitably incorporated into synthetic base oils such as alkyl esters of dicarboxylic acids, polyglycols and alcohols, polyalphaolefins, alkyl benzenes, organic esters of phosphoric acids, polysilicone oils, etc.
Natural base oils include mineral lubricating oils which may vary widely as to their crude source, e.g., whether paraffinic, naphthenic, mixed, paraffinic-naphthenic, and the like; as well as to their formation, e.g., distillation range, straight run or cracked, hydrorefined, solvent extracted and the like.
More specifically, the natural lubricating oil base stocks which can be used in the compositions of this invention may be straight mineral lubricating oil or distillates derived from paraffinic, naphthenic, asphaltic, or mixed base crudes, or, if desired, various blends oils may be employed as well as residuals, particularly those from which asphaltic constituents have been removed. The oils may be refined by conventional methods using acid, alkali, and/or clay or other agents such as aluminum chloride, or they may be extracted oils produced, for example, by solvent extraction with solvents of the type of phenol, sulfur dioxide, furfural, dichlorodiethyl ether, nitrobenzene, crotonaldehyde, molecular sieves, etc.
The compositions of the invention can also be employed in gasoline, gasohol and in middle distillate fuels such as diesel fuel, furnace oil and jet fuel.
The invention is further illustrated by, but is not intended to be limited to, the following examples wherein parts and percentages are by weight unless otherwise indicated.